package thinkingInJava.io;
// page 564 对比内存映射（MappedByteBuffer ）与普通读写的效率
//: io/MappedIO.java
import java.nio.*;
import java.nio.channels.*;
import java.io.*;

public class MappedIO {
	private static int numOfInts = 4000000;
	private static int numOfUbuffInts = 200000;
	private abstract static class Tester {
		private String name;
		public Tester(String name) { this.name = name; }
		public void runTest() {
			System.out.print(name + ": ");
			try {
				long start = System.nanoTime();
				test();
				double duration = System.nanoTime() - start;
				System.out.format("%.2f\n", duration/1.0e9);
			} catch(IOException e) {
				throw new RuntimeException(e);
			}
		}
		public abstract void test() throws IOException;
	}
	private static Tester[] tests = {
			new Tester("Stream Write") {
				public void test() throws IOException {
					DataOutputStream dos = new DataOutputStream(
							new BufferedOutputStream(
									new FileOutputStream(new File("temp.tmp"))));
					for(int i = 0; i < numOfInts; i++)
						dos.writeInt(i);
					dos.close();
				}
			},
			new Tester("Mapped Write") {
				public void test() throws IOException {
					FileChannel fc =
							new RandomAccessFile("temp.tmp", "rw")
							.getChannel();
					IntBuffer ib = fc.map(
							FileChannel.MapMode.READ_WRITE, 0, fc.size())
							.asIntBuffer();
					for(int i = 0; i < numOfInts; i++)
						ib.put(i);
					fc.close();
				}
			},
			new Tester("Stream Read") {
				public void test() throws IOException {
					DataInputStream dis = new DataInputStream(
							new BufferedInputStream(
									new FileInputStream("temp.tmp")));
					for(int i = 0; i < numOfInts; i++)
						dis.readInt();
					dis.close();
				}
			},
			new Tester("Mapped Read") {
				public void test() throws IOException {
					FileChannel fc = new FileInputStream(
							new File("temp.tmp")).getChannel();
					IntBuffer ib = fc.map(
							FileChannel.MapMode.READ_ONLY, 0, fc.size())
							.asIntBuffer();
					while(ib.hasRemaining())
						ib.get();
					fc.close();
				}
			},
			new Tester("Stream Read/Write") {
				public void test() throws IOException {
					RandomAccessFile raf = new RandomAccessFile(
							new File("temp.tmp"), "rw");
					raf.writeInt(1);
					for(int i = 0; i < numOfUbuffInts; i++) {
						raf.seek(raf.length() - 4);
						raf.writeInt(raf.readInt());
					}
					raf.close();
				}
			},
			new Tester("Mapped Read/Write") {
				public void test() throws IOException {
					FileChannel fc = new RandomAccessFile(
							new File("temp.tmp"), "rw").getChannel();
					IntBuffer ib = fc.map(
							FileChannel.MapMode.READ_WRITE, 0, fc.size())
							.asIntBuffer();
					ib.put(0);
					for(int i = 1; i < numOfUbuffInts; i++)
						ib.put(ib.get(i - 1));
					fc.close();
				}
			}
	};
	public static void main(String[] args) {
		for(Tester test : tests)
			test.runTest();
	}
} /* Output: (90% match)
Stream Write: 0.56
Mapped Write: 0.12
Stream Read: 0.80
Mapped Read: 0.07
Stream Read/Write: 5.32
Mapped Read/Write: 0.02
 *///:~

